LMS-1947 Better error messages.

...cisd/etlserver/entityregistration/RegistrationStatus.java

...ityregistration/SampleAndDataSetControlFileProcessor.java

...registration/SampleAndDataSetRegistrationGlobalState.java

...tityregistration/SampleAndDataSetRegistrationHandler.java

...erver/entityregistration/SampleAndDataSetRegistrator.java

...registration/SampleAndDatasetRegistrationHandlerTest.java

...ration/test-data/not-all-subfolders-mentioned/control.tsv